In a fuel cell, hydrogen serving as fuel is circulated for reuse. When a fuel cell is used as a power source for an electric automobile, a purging operation is sometimes performed to discharge a part of the hydrogen in the circulation system outside. For example, a purging operation is required to restore the fuel cell voltage when the voltage drops temporarily, or to reduce a difference in pressure between the electrodes of the fuel cell arising when the vehicle is stationary.
When the hydrogen in the circulation system is to be discharged outside in a purging operation, a diluter is used to dilute the hydrogen with air so that the hydrogen concentration is reduced below its combustion limit. For example, Japanese Patent Application Publication No. 2003-132915 discloses a technique of diluting hydrogen off-gas to or below this concentration by retaining the purged hydrogen off-gas in a tank and gradually mixing the hydrogen off-gas with air which passes through an adjacent tank (Patent Document 1).
Patent Document 1: Japanese Patent Application Publication No. 2003-132915 (FIG. 2 etc.)
Patent Document 2: Japanese Patent Application Publication No. 2000-348743 (paragraph number 0029, FIG. 2, etc.)
Patent Document 3: Japanese Patent Application Publication No. 2002-289237 (FIG. 8 etc.)